Method for on board decarbonization of hydrocarbon fuels in a vehicle

ABSTRACT

A method and apparatus for the reduction of carbon dioxide emissions by the on-hoard treatment of a portion or all of the hydrocarbon fuel used to power an internal combustion engine mounted in a conventional transportation vehicle, utilize known decarbonization technology to break the fuel&#39;s hydrogen-carbon bond. The compounds are then cooled and separated into (1) elemental carbon powder that is stored on-board for later recovery and industrial use, and (2) hydrogen, or a hydrogen-rich gas stream, that is burned as a fuel in the ICE and/or diverted to other on-board energy related applications.

FIELD OF THE INVENTION

This invention relates to the reduction of carbon dioxide (CO₂)emissions from internal combustion engines (ICE) used to powerautomotive and other vehicles by the on-board treatment of gaseousand/or liquid hydrocarbon fuels.

BACKGROUND OF THE INVENTION

There are growing concerns about the apparent relationship of increasingthe concentration of greenhouse gases and the global warming phenomenon.As a consequence, a broad consensus has developed as to the need toreduce CO₂ emissions associated with various human activities.

Carbon dioxide emissions (CO₂) from hydrocarbon-fueled transportationvehicles powered by internal combustion engines (ICE) constitute asignificant part of the total man-made greenhouse gas emissions. As aresult, adoption of new rules to significantly reduce CO₂ from vehiclesare currently being considered in many countries around the world. As anexample, action was recently taken by the State of California to adoptnew regulations that require significant reductions in CO₂ emissionsfrom road vehicles by the year 2016.

Emissions of CO₂ from stationary energy sources such as power plants canbe efficiently separated and captured either ahead of, or after thecombustion process using processes and apparatus known in the art. Thesetechniques are impractical in the case of mobile vehicular systems suchas automobiles, trucks and buses, principally due to the associated highcost and limited availability of on-board space. Current efforts toaddress the need to reduce CO₂ emissions from mobile systems, such astransport vehicles, involve optimization of fuel economy throughmeasures that include enhancing the efficiency of the combustion engineand the power train, adoption of more fuel-efficient power trains (e.g.,hybrids), and the reduction of rolling and drag losses.

All of these steps taken together have resulted in a measurablereduction of CO₂ emissions from automobiles. However, the extent ofthese reductions may not be sufficient to maintain an acceptable levelof CO₂ emissions in view of the rapidly growing automotivetransportation sector. Because of these concerns, alternative propulsionsystems using non-carbon or carbon-neutral fuels have been given seriousconsideration and it has been urged by some that they gradually replacecurrent hydrocarbon-fueled ICE-based systems. These alternative systems,however, will require substantial alterations to the transportationfueling infrastructure that has been developed on a worldwide basis overthe past century.

Various strategies have been proposed for reducing the production of CO₂entering the atmosphere to mitigate global warming. Decarbonization offossil fuels has been identified with the process of removing carbonbefore or after combustion. Fossil Fuel Decarbonization Technology forMitigating Global Warming, Brookhaven National Laboratory (1997-98).

It has been proposed that natural gas be subjected to thermaldecomposition, or pyrolysis, in the absence of air for the production of(1) hydrogen as a clean-burning fuel or feed stream to fuel cells and(2) carbon black, which is a form of elemental carbon. Hydrogen fromNatural Gas Without Release of CO₂ to the Atmosphere, Int'l S. HydrogenEnergy, Vol. 23, No. 12, pp. 1087-1093 (1998). The thermal decompositionin this case is achieved by a plasma arc process that utilizeselectricity to form the plasma using hydrogen.

A process for the thermocatalytic decomposition of hydrocarbons intohydrogen and elemental carbon in the absence of air has been disclosed.Thermocatalytic CO₂-Free Production of Hydrogen from Hydrocarbon Fuels,N. Muradov, Proceedings of the 2002 U.S. DOE Hydrogen Program Review,NREL/CP-6 10-32405. The reaction is catalyzed by the carbon particlesproduced in the process.

A process for methane decomposition in the presence of a small amount ofoxygen in an auto-thermal regime was disclosed by N. Muradov in akeynote paper presented at the 2nd European Hydrogen Energy Conference,Spain, November 2005. This process uses activated carbon as a catalystfor the decomposition reaction.

SUMMARY OF THE INVENTION

The present invention broadly comprehends a method and apparatus thatutilizes a decarbonization unit on board the vehicle adjacent to theengine used to power automotive and other types of vehicles thatconstitute a hydrocarbon-based transportation system. Thedecarbonization unit treats a portion or all of the fuel and separates aportion of the carbon from the hydrocarbon fuel used to power the ICE,separates the produced hydrogen or hydrogen-rich gas from the carbonparticles and temporarily stores the carbon on board the vehicle.

The carbon is extracted in the form of elemental carbon powder. Thecarbon preferably is in the form of a powder, that is, it is of a veryfine or small particle size. Various scrapers or other particledisaggregating devices can be used downstream or included as a part ofthe separator to achieve this result. The stored carbon is withdrawnfrom the vehicle periodically, e.g., at refueling stations, andeventually transported to a central storage area or directly to anindustrial user. The carbon itself is a relatively high-value materialthat can be used in the manufacture of tires, plastics, paints, inks,steel, gaskets, and a wide variety of other products.

Alternatively, part of this produced carbon can be used to power acarbon-based fuel cell that serves as an on-board auxiliary powergenerating unit to satisfy some or all of the vehicle's electrical powerrequirements.

The hydrogen or hydrogen-rich gas that has been separated from thecarbon can be fed to the ICE, increasing the fuel's overallhydrogen-to-carbon ratio. This will result in a reduction in CO₂emissions, and will also have a positive effect on the vehicle's overallfuel combustion efficiency.

The hydrogen generated can also be utilized for other on-boardapplications, such as powering a fuel cell-based auxiliary power unitthat will also contribute to enhanced fuel efficiency and which wouldotherwise require a dedicated on-board fuel reformer.

A portion of the hydrogen separated from the fuel can also be used inthe after-treatment of the exhaust gases from the ICE. In oneembodiment, the hydrogen, or hydrogen-rich gas, is employed as areducing agent for a hydrogen-based selective catalytic reduction (SCR)after-treatment system for nitrogen oxides, or NOx, emissions from theICE.

The present invention produces a method of limiting CO₂ emissions fromICE-based transportation systems that requires a relatively modestmodification to the existing infrastructure. The fuels treated in thedecarbonization unit can be any hydrocarbon fuel used for transportationvehicles including gasoline, diesel, naphtha, ethanol, natural gas, andblends of two or more of these fuels.

Carbon storage and collection systems, including pumps and conduits, arecurrently available and can be installed at existing fueling stations.Instead of being a liability, the carbon (which constitutes the majorportion of hydrocarbon fuels) is separated by this invention in the formof a useful material that can be used as a feedstock for importantdomestic and international manufacturing industries, or as a fuel orfuel extender for boilers, gasifiers and industrial furnaces. Theimplementation of this invention will eliminate the need for a costlytransition to alternative carbon-free fueling infrastructure, and willcreate new business opportunities for establishing a parallelcarbon-based industry.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described below with reference to theattached drawings in which:

FIG. 1 is a schematic diagram illustrating a first preferred embodimentof the arrangement of apparatus for practicing the method of theinvention on board an automotive vehicle; and

FIG. 2 is a schematic diagram similar to FIG. 1, and illustrating asecond preferred embodiment of apparatus and a method for the practiceof the invention on board an automotive vehicle.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a conventional hydrocarbon fuel, e.g., gasoline ordiesel, flows from fuel tank 1 to fuel system distribution valve 2 thatfunctions in conjunction with microprocessor/controller 3 to regulatethe flow of fuel and distribute it to internal combustion engine 13through fuel line 4 and/or to decarbonization unit 6 through fuel line5. The flow of fuel is based on an optimized fuel distribution schemeprogrammed in control unit 3.

The decarbonization unit 6 of the present invention, by definition,consists of four major components, namely a decomposer 7, a cooling unit8, a separator 9 and a carbon storage unit 11.

In the first embodiment, shown in FIG. 1, all or a portion of the fuelis fed to the decomposer 7 where it decomposes or cracks in the absenceof air, thereby producing elemental carbon and hydrogen. Depending uponthe thermal decomposition efficiency, it is possible that gaseoushydrocarbon compounds will be produced along with the hydrogen. Thesegaseous hydrocarbon compounds can include methane, ethane, and traces ofC₃ compounds. Where the fuel contains oxygenates, the thermaldecomposition products will include CO and CO₂.

The fuel supplied to the decomposer 7 is vaporized, either before orinside the decomposer 7. The thermal decomposition can be achieved bythermocatalysis, a plasma process, or other industrial decompositionprocesses known to, or to be developed by the art. The heat necessaryfor the decomposition will be provided by an external source such aselectricity, hot exhaust gases, a dedicated burner, or other meanspresently known in the art or to be developed. The thermocatalyticdecomposition process has the advantage of operating at a relativelylower temperature than other non-catalytic decomposition processes.

The carbon and hydrogen, or hydrogen-rich gas, are transported to cooler8 for cooling, and then moved to separator 9, which separates the solidelemental carbon in a powdery form from the gaseous hydrogen orhydrogen-rich gas. The carbon is transported from separator 9 throughline 10 to storage unit 11 that has a capacity conforming to thevehicle's refueling intervals. The storage unit 11 is provided with anaccess port or outlet 15 for periodically unloading the carbon.

The hydrogen, or hydrogen-rich gas, from the separator 9 is passedthrough line 12 and is fed to internal combustion engine 13 and/or usedfor other purposes. Hydrogen, or hydrogen-rich gas, is introduced tocombustion engine 13 either through the intake manifold where it mixeswith intake air or an intake air/fuel mixture, or through a specialinjector that injects it directly into the combustion chamber.

In the second embodiment, as illustrated schematically in FIG. 2, thefuel coming from fuel system 2 through line 5 is vaporized and mixedwith a controlled amount of air (17) in the mixing unit 16. Thisair-fuel mixture (18) is then fed to decomposer 7 in decarbonizationunit 6 where exothermic combustion and endothermic decomposition occursimultaneously using catalytic or non-catalytic media. In this process,the heat released by the partial oxidation reaction will provide all orpart of the heat necessary to achieve the thermal decomposition of thehydrocarbon fuel into carbon and a hydrogen-rich gas stream.

The ratio of the air-fuel mixture introduced into decomposer 7 isadjusted in order to achieve the desired decomposition temperature.External heating, such as the passage of hot exhaust gases through aheat exchanger, can be employed, if necessary, to supplement theinternal heating in order to minimize the fuel energy penalty.Thereafter, the temperature is reduced in cooler 8, the carbon isseparated from the hydrogen and other gases, and the process proceeds asdescribed above in connection with the first embodiment and FIG. 1.

Feeding the produced hydrogen or hydrogen-rich gas to the internalcombustion engine will improve the fuel combustion efficiency and willhave the desirable effect of further reducing carbon emissions.

In a further preferred embodiment illustrated in FIGS. 1 and 2, aportion of the extracted hydrogen, or hydrogen-rich gas can be also usedto a power fuel cell-based auxiliary power unit 20, which is anefficient on-board electrical power generation device. Specifically, thehydrogen can be used to power hydrogen-based auxiliary power unit 20 viafeed line 23 in conjunction with 3-way valves 25. If necessary, hydrogencan be selectively recovered from any hydrocarbon gases that are presentdownstream of separator 9 by utilizing methods and apparatus known inthe art in order to provide a hydrogen feedstream to on-board fuel cell20. Additionally, a portion of the hydrogen can be utilized to operate ahydrogen-based after-treatment system 24, or for other purposes thatwill be apparent to those of ordinary skill in the art.

In a further preferred embodiment, a portion of the separated carbon canbe fed via 3-way valve 25 and line 21 to a carbon-based auxiliary powergeneration unit 22 on board the vehicle. The output of power unit 22 canbe used to meet the vehicle's energy requirement and reduce or eliminatethe need to operate the vehicle's alternator/generator, therebyimproving fuel efficiency.

The invention thus utilizes a novel method to extract a portion of thefuel's carbon content on-board the transportation vehicle resulting in adecrease in carbon dioxide emissions from the vehicle's ICE.

The carbon is extracted in the form of elemental carbon which is ahigh-value industrial feedstock. It is also in the form of a powderwhich is safe, easy to collect, store, transport and distribute.Elemental carbon has a significant heating value, e.g., 33.8 MJ/kgcompared to 44 MJ/kg for fuel oil, and can be used as a combustible fuelor fuel extender in boilers, gasifiers and industrial furnaces. When thecarbon is used in this manner, it will be understood that the inventiontransfers a portion of the carbon emissions from mobile sources to astationary source where other means well known in the art can be appliedto control carbon dioxide emissions.

As will be apparent to one of ordinary skill in the art, the calculationof the so-called fuel energy penalty, or energy loss, associated withthe decarbonization of the engine's fuel in accordance with theinvention is based upon a number of variables and assumptions. Thesevariables include the type of fuel, since different fuels have differentheating values. The heat that is available for recovery and transferfrom the exhaust of the ICE will also vary with the type of fuel beingburned and conditions of operation. The size and configuration of theheat exchanger will affect its efficiency. Each type of decomposer 7 hasdifferent energy requirements and will operate at differentdecarbonization efficiencies, and these efficiencies will vary for thesame apparatus depending upon the type of fuel being decarbonized.However, regardless of the type of decomposer utilized, the beneficialresult of reducing the carbon dioxide emissions from the ICE will beachieved.

It will also be understood by those of ordinary skill in the art thatwhile achieving a 100% conversion rate to hydrogen with thedecarbonization process is theoretically possible, in actual practicethe conversion will also produce some measurable proportion ofhydrocarbon gases.

The following economic analysis demonstrates that on-board partialdecarbonization of hydrocarbon fuel is viable process to effectivelyreduce carbon emissions with a minimal or no adverse financial effect.This example is based on a 25% on-board decarbonization of a gasolinefuel that has an average molecular structure of C_(n)H_(1.86n) and ahigher heating value of 47 MJ/kg. Consequently, the carbon to hydrogenmass ratio is 6.4 to 1, the carbon mass ratio in gasoline is 0.865, andthe hydrogen mass ratio in gasoline is 0.135. For the purpose of thisanalysis, a complete decomposition of gasoline into elemental carbon andhydrogen is assumed.

The total decrease in fuel energy attributable to decarbonization willbe equal to the sum of the energy content of the extracted carbon plusthe energy required for the fuel decomposition. The energy decrease inthe fuel attributable to 25% decarbonization per each one kg of fuel,where carbon has a heating value of 33.8MJ/kg, is calculated as follows:

0.25×0.865 kg C×33.8 MJ/kg C=7.309 MJ  (1)

The energy required for decomposing the gasoline in this example isestimated to be 1.073 MJ/kg. For 25% decarbonization of 1 kg of fuel,this energy will be equal to:

0.25 kg×1.073 MJ/kg=0.268 MJ  (2)

Therefore, the total energy reduction per each kg of fuel as a result of25% decarbonization is:

Unutilized Carbon Energy+Decomposition Energy=7.309 MJ+0.268 MJ=7.577MJ  (3)

The energy loss percentage per total energy value theoreticallyavailable from 1 kg of the fuel in this example is:

7.577 MJ÷47 MJ=16%  (4)

Conducting the same analysis on methane will yield a percentage ofenergy loss equal to 13% for the 25% decarbonization case. For dieselfuel, this percentage should be close to that of gasoline.

A portion of this energy loss will be recovered by the hydrogenenrichment positive effect on the fuel combustion efficiency of the ICEas reported by recent studies such as those conducted at MIT and Delphi(SAE Papers 2005-01-0251 & 2003-01-1356). MIT reported up to 12%enhancement of fuel combustion efficiency due to hydrogen enrichment,while Delphi results indicated up to 24% fuel consumption decrease dueto combined effect of hydrogen enrichment and utilization of fuel-cellbased auxiliary power unit. As an added benefit, it is also reportedthat hydrogen enrichment will dramatically reduce the formation ofnitrogen oxides (NOx).

As reported by recent studies, using a portion of the hydrogen producedby the decarbonization unit to power a fuel cell-based auxiliary powerunit will also improve the overall fuel efficiency, thereby furthercompensating for the energy reduction of decarbonization.

In certain cases, the energy requirements for the fuel decompositionprocess can be significantly reduced by using the heat of the engine'sexhaust gases to raise the temperature of the fuel that is to bedecomposed.

The recovered carbon also has a dollar value that is applicable tocompensate for the value of the lost energy and to cover the expensesassociated with any infrastructure investments, transportation costs,handling and storage. The value of the carbon will be dependent on itsquality and structure which vary mainly depending on the fuel type andthe decomposition process. Based on the results published for methanedecomposition, the carbon produced using thermocatalytic decompositionprocess is expected to be dominated by amorphous and crystallinegraphite, of which the price ranges from $0.22-0.41 per kg [SRIInternational, Chemical Economics Handbook, 1997]. Plasma decompositionis expected to yield amorphous forms of carbon, e.g., carbon black whichis priced in the range of $0.66-1.08 per kg [Chemical MarketingReporter, 2001; Chemical Week, 2001].

In an average passenger car with 75-liter fuel tank, 25% decarbonizationcan be expected to produce about 12 kg of elemental carbon. The dollarvalue of this amount of carbon will be about $3.60 for graphitic carbon(assuming an average price of $0.30/kg), and about $9.60 for carbonblack (assuming an average price of $0.80/kg).

The reduction in carbon dioxide emissions will also by itself, representan economic opportunity for countries participating in the Kyotoprotocol. A credit for CO₂ emission reduction by this invention can beclaimed for a Clean Development Mechanism (CDM) project.

In summary, the current invention will result in a loss of some of thefuel energy, depending upon the scale of the decarbonization process.However, this energy loss can be minimized by taking into account thehydrogen enrichment effect, utilizing on-board fuel cell auxiliary powergeneration, and recovery of heat energy from exhaust gases for use inthe decomposition process. In addition, part or all of this loss iscompensated for by the value of the elemental carbon recovered and theCO₂ credit associated with Kyoto Protocol CDM projects or otherapplicable environmental regulatory schemes.

This analysis establishes that the partial decarbonization process ofthe invention is viable for use in an average passenger car. Theeconomics improve for larger vehicles where more space is available, theintervals between refueling are longer, and the efficiency improvementdue to utilization of an auxiliary power unit is foreseeably greater.

As will be apparent to one of ordinary skill in the art, the modes ofoperation utilizing the method and apparatus of the invention can bevaried to meet the specific needs of the particular type and even modelof transport vehicle, whether it be a car, truck, bus, train, ship, orother conveyance. In all such instances, it will also be apparent thatthe goal of reducing CO₂ emissions from the ICE will be achieved by thepractice of the invention.

Thus, the scope of the invention is not to be determined solely withreference to the general description and the specific embodiments setforth above and in the drawings, but by the interpretation of the claimsthat follow.

1. A method for the reduction of emissions of CO2 from a vehicle poweredby a hydrocarbon fuel-burning internal combustion engine (ICE) bysubjecting at least a portion of the fuel to on-board decarbonization,the method comprising: (a) providing an on-board decarbonization unitthat includes a decomposer, a cooler, a separator and a storage unit;(b) feeding a gaseous or vaporized liquid hydrocarbon fuel to thedecomposer on board said vehicle to thereby cause said fuel to decomposeand to produce hydrogen or a hydrogen-rich gas, and elemental carbon;(c) subjecting the hydrogen or the hydrogen rich-gas, and the carbon tocooling in an on-board heat exchanger; (d) separating the hydrogen orhydrogen-rich gas from the carbon in the separator; (e) transferring theseparated carbon from the separator to on-board storage unit; and (f)delivering the hydrogen or hydrogen-rich gas to the vehicle's ICE foruse as fuel.
 2. The method of claim 1, wherein the decomposition of saidfuel in said decomposer is effected by a decomposition process selectedfrom the group consisting of a thermocatalytic decomposition process, aplasma decomposition process, an auto-thermal catalytic decompositionprocess, and a super-adiabatic combustion process.
 3. The method ofclaim 1, wherein the heat required for the decomposition of the fuel isprovided from an external source selected from the group consisting ofelectricity, hot exhaust gases, a dedicated burner, and combinationsthereof.
 4. The method of claim 1, wherein the hydrogen or hydrogen-richgas is delivered to the vehicle's ICE for mixing with intake air or anair/fuel mixture, or injected directly into the combustion chamber, toenhance the engine's combustion efficiency.
 5. The method of claim 1,wherein a portion of the hydrogen or hydrogen-rich gas is employed as areducing agent for a hydrogen-based selective catalytic reduction (SCR)after-treatment of nitrogen oxide (NO_(x)) emissions from the vehicle'sICE.
 6. The method of claim 1, wherein the hydrogen or the hydrogen-richgas is employed to operate a hydrogen-based fuel cell as an on-boardauxiliary power unit, to thereby provide electrical energy for thevehicle's electrical requirements.
 7. The method of claim 1, wherein thecarbon separated in step (d) is employed to operate a carbon-based fuelcell as an on-board auxiliary power unit, to thereby provide electricalenergy for the vehicle's electrical requirements.
 8. The method of claim1, wherein the carbon recovered from the vehicle is processed for use asa feedstock in the manufacture of tires, in metallurgical processes,toners, inks, paints, seals and gaskets, as a fuel or fuel extender forboilers, gasifiers and industrial furnaces.
 9. The method of claim 1 inwhich up to 100% of the fuel utilized to power the vehicle is treated inthe on-board decarbonization unit.
 10. The method of claim 1 in whichthe fuel entering the decarbonization unit is any hydrocarbon fuel usedfor transportation vehicles including gasoline, diesel, naphtha,alcohol, natural gas, and blends of two or more of these fuels.
 11. Themethod of claim 1 in which the separator is selected from gas/solidseparation cyclones, membranes, and filtration systems.
 12. The methodof claim 1 which includes an electronic control unit programmed with anoptimized fuel distribution scheme by which the fuel flow rates to thedecarbonization unit and to the internal combustion engine are adjusted.13. The method of claim 12 which further includes controlling the flowof hydrogen or hydrogen-rich gas produced by the decarbonization unit tothe internal combustion engine and/or to other uses including thehydrogen-based fuel-cell auxiliary power unit and hydrogen-basedafter-treatment.
 14. The method of claim 12 which further includescontrolling the flow of a portion of the separated carbon produced inthe decarbonization unit to an on-board carbon-based fuel-cell auxiliarypower unit.
 15. The method of claim 1 which includes the further stepsof: (g) mixing the hydrocarbon fuel with air to provide an air/fuelmixture upstream of the decomposer; (h) introducing the air/fuel mixtureinto the decomposer under conditions to effect simultaneous exothermicpartial oxidation reaction and endothermic decomposition of thehydrocarbon fuel, thereby producing elemental carbon and a hydrogen-richgas.
 16. The method of claim 15 in which a catalytic decompositionprocess or a super-adiabatic combustion process is utilized to achievethe simultaneous partial oxidation and thermal decomposition of thefuel, wherein the heat released from partial oxidation provides all orpart of the heat needed for decomposition.
 17. The method of claim 15 inwhich external heating, such as heat from the engine's exhaust gases, isutilized in conjunction with internal heating to maximize the heatefficiency usage.
 18. An apparatus for the reduction of emissions of CO₂from a hydrocarbon fuel-burning internal combustion engine (ICE) used topower a vehicle, the apparatus comprising an on-board decarbonizationunit that includes: (a) a decomposer that decomposes vaporized fuel toproduce hydrogen or a hydrogen-rich gas, and elemental carbon; (b) acooler in fluid communication with the decomposer for cooling thehydrogen or the hydrogen rich-gas, and the carbon by heat exchange; (c)a separator in fluid communication with the cooler for receiving thecooled hydrogen or hydrogen-rich gas and carbon and separating thehydrogen or hydrogen-rich gas from the carbon; (d) an on-board carbonstorage unit in communication with the separator for receiving separatedcarbon; and (e) means for delivering the hydrogen or hydrogen-rich gasfrom the separator to the vehicle's ICE for use as a decarbonized fuel.19. The apparatus of claim 18, wherein the decomposer utilizes adecomposition process selected from the group consisting of athermocatalytic decomposition process, a plasma decomposition process,an auto-thermal catalytic decomposition process, and a super-adiabaticcombustion process.
 20. The apparatus of claim 18 which includes amicroprocessor and an electronic control unit having an optimized fueldistribution program by which the fuel flow rates from an on-boardhydrocarbon fuel storage tank to the decarbonization unit and to theinternal combustion engine are adjusted to meet the operationalrequirements of the vehicle.